FIG. 1 is a schematic view of the general design of a binocular 2. The latter are made of two housing halves or tubes (4a, 4b) which are arranged parallel to one another and each contain an optical system with the result that a left-hand and a right-hand telescope (6a, 6b) are formed, and a bridge 8 which connects the two housing halves.
The respective optical system (10a, 10b) is made of at least one objective lens unit (12a, 12b), a prism system (14a, 14b) and an eyepiece (16a, 16b). An optical axis is defined in each case by the objective lens unit and by the eyepiece.
The objective lens unit (12a, 12b) can be made of a plurality of individual lenses or cemented elements.
For the purpose of focusing an object 18 which is being viewed through the binocular 2, in each case at least one optical element of the left-hand and right-hand telescopes (6a, 6b) is displaced axially. For this purpose, for example the eyepiece (16a, 16b) can axially displace the entire objective lens unit (12a, 12b) or a lens or lens group which can be a part of the objective lens unit. The latter lens or lens group is typically arranged between the fixed objective lenses and the prism system (14a, 14b) and is typically referred to as a focusing lens. For the purpose of focusing, in one specific design a rotary knob 22 is arranged on a central axis A with which synchronous axial displacement of the left-hand and right-hand focusing lenses is driven. This arrangement is also referred to as a central drive.
The objective lens unit (12a, 12b) can produce a real image which is inverted relative to the viewed object 18, in an image plane which is assigned to the objective lens unit (12a, 12b). For the purpose of image erection the prism system (14a, 14b) can be constructed, for example, according to Abbé-König, Schmidt-Pechan, Uppendahl, Porro or some other prism system variant. Via the prism system (14a, 14b), the image which is inverted is placed in an upright position again and is presented in a new image plane, the intermediate image plane.
A field diaphragm (13a, 13b) which sharply delineates the field of vision can be located in the intermediate image plane. The eyepiece (16a, 16b) can be used to represent the image of the intermediate image plane at any desired distance, for example into infinity or an apparent distance of one meter.
A beam direction is typically defined by the sequence object 18—object lens unit (12a, 12b)—prism system (14a, 14b)—eyepiece (16a, 16b)—eye (24a, 24b).
The optical axis (26a, 26b) of the objective lens unit can have a lateral offset as a result of a beam offset owing to the prism system (14a, 14b) with respect to the optical axis (28a, 28b) of the eyepiece (16a, 16b).
In order to adapt the lateral distance between the eyepieces to the interval distance between the pupils (25a, 25b) of the user's eyes, the so-called distance W between the eyes, the bridge 8 of the binocular 2 can be embodied as what is referred to as a folding bridge 8. In the binocular 2 with a folding bridge 8 the two housing halves (4a, 4b) and therefore the entire optical system (10a, 10b) which is arranged in the left-hand and right-hand housing halves, including all the optical elements (12a, 14a, 16a, 12b, 14b, 16b) of the left-hand and right-hand telescopes (6a, 6b) are joined to one another in a pivotable fashion via a joint 30 of the folding bridge 8. As a result, the distance between the eyepieces can be adapted to the individual distance W between the eyes by the user via the pivoting movement of the two housing halves (4a, 4b). A typical interval for the adjustment of the distance between the eyepieces can be in the range from approximately 55 mm to 75 mm.
The aperture diaphragm can be formed either by a mount of an optical element or can be defined by a separate diaphragm. It can be imaged into a plane by the rest of the optical system which follows in the beam direction, said plane being located behind the eyepiece in the beam direction, typically at a distance of 5 to 25 mm from said eyepiece. This plane is typically referred to as the plane of the exit pupil.
A different type of defective vision of the user's two eyes can be taken into account via a diopter compensation. For this purpose, for example the relative axial positions of the focusing lenses of the two telescopes (6a, 6b) relative to one another can be adjusted by the user. Another possibility is to be able to modify the axial positions of the two eyepieces (16a, 16b) relative to one another, for example by adjusting just one of the two eyepieces.
In order to protect the user against lateral incident light, eye cups which can be pulled out, turned out or folded over can be provided on the eyepieces (16a, 16b).
Furthermore, binocular 2 can contain further optical components which serve, for example, to stabilize an image, input beams or output beams or for photographic purposes. Likewise, electronic components, operator control elements or energy stores may be provided which are necessary for the specified purposes.
Securing devices, to which, for example, a strap for carrying can be attached, can usually be located on the side of the binocular 2.
In the case of a binocular with a central drive and diopter compensation on one of the two eyepieces the user usually only sets the diopter compensation once at the start in order to adapt the relative focusing of the two telescopes (6a, 6b) to the relative refractive power of his or her two eyes (24a, 24b). Afterwards, the user can then use the central focusing drive element which is formed here as a rotary knob 22 to focus the two telescopes (6a, 6b) synchronously with the changing distance of objects 18 to be observed. In the case of binocular 2 with a folding bridge 8 the focusing drive is one of the critical parts. Care should be taken to ensure that the diopter compensation does not unintentionally adjust itself during use, in particular during pivoting or “folding” of the folding bridge 8.
A binocular with a focusing drive which meets this requirement is described in U.S. Pat. No. 4,630,901. Here, an objective-lens-unit-side adjustment knob drives a central driver disk which is guided linearly in a guide pin. Two push rods, which engage in the objective lens unit mount are coupled into the driver disk.
Although such focusing drives typically meet the requirements which are made, the simplicity, robustness and lever ratio of pushrod mechanisms or lever mechanisms basically leave room for improvement. It should also be ensured that sticking of the focusing drive can be effectively prevented. In addition, many mechanisms take up a relatively large amount of space.